1. Field of the Invention
The present invention concerns an optical system for the color reproduction of video images. More specifically, it concerns an optical system of the kind comprising a light source, a color electro-optical modulator composed of pixels linked to the colors red, green, and blue respectively, and optical collimation means used to illuminate the modulator.
2. Discussion of the Background
Optical systems of this kind gay be used either inside a device for the large-screen projection of color video images, termed a videoprojector, or for direct viewing. In the first instance, the optical system is linked conventionally to a condensing lens, a lens, and a screen. In the second case, it preferably comprises a diffuser positioned downstream from the electro-optical modulator.
The main disadvantage of the optical systems of this type currently used, in particular videoprojectors, is the weak luminosity of the image obtained. In fact, in the case of a videoprojector, the luminous flow reaching the screen is at most 150 lumens for a source generating 1,200 lumens. This low luminance is mainly the result of the polarization of the luminous wave lighting the modulator, and also of the color filtering, which reduces luminance by approximately one-third.
To overcome this difficulty, it has been suggested that, particularly in videoprojectors, the primary components of the luminous source be dispersed using dichroic mirrors. However, this technique requires the use of four dichroic mirrors and of three electro-optical modulators, each of which modulates one of the primary components. This arrangements leads to mechanical adjustment problems. Moreover, the apparatus thus created has a relatively large focal length.